As an agnostic, I think that both theists and atheists have reasons, some of them good, for believing what they do. It’s not just thoughtlessness or blind faith that causes someone to declare for theism or atheism.

My issue is with what I would call confidence theism and confidence atheism.

If you are a confidence theist or confidence atheist, you too often focus on confirmation bias (counting the hits and ignoring the misses surrounding your pet theory), and take an excess of pleasure in huddling with your favored community. You may also demonstrate commitment to your group by desecrating the beliefs of others. You might do this by blasphemy, argument, or even iconoclasm (disrespecting or destroying the sacred icons or objects of an outside group, as when the atheist PZ Myers desecrated a Catholic host). In other words, you might declare, not just great confidence in your own side’s dogmas, but enormous contempt for alternative views–and the people who hold them.

So a confidence theist or a confidence atheist reads mostly the books of his or her own tribe, will posture as 100% certain that he’s right, and will be derisive of outsiders.

It’s human nature to behave this way, but the following Bayes’ Rule inspired questions cut through a lot of this static. Bayes’ Rule mathematically formalizes, in terms of probability, these five put-up-or-shut-up questions:

What probability do you assign to claim x actually being true? In other words, on a grayscale of 1-100 (100 being that you’re completely certain), where do you rate your claim?

Why do you give this claim that level of confidence?

Why do you think it’s the best claim among the options?

Is there an alternative claim that you take to be at least somewhat competitive with your own claim? Which one?

What sorts of new data points, appearing in the future, might cause you to have less confidence in your claim, or even to adopt one of the alternative claims?

These five questions tamp down unwarranted posturing and confidence–this impulse to act as if you’re 100% certain about a matter–and 100% certain that another person is wrong.

Bayes, in my view, is healthy for everyone to practice (theist, agnostic, and atheist). It tones down the hostile energy (or ought to). It makes the conversation more honest and measured.

And it historicizes claims. It reminds us all that we’re limited, evolved, and contingent creatures reasoning in space and time, and that space and time might therefore bring us to surprises.